The majority of electrodes used in electric arc furnaces are self-baking electrodes, so called Söderberg electrodes. A self-baking electrode consists of an electrode casing extending from the top of the electrode to below electrode contact shoes in the furnace, and an electrode portion which initially consists of a carbon based paste in the electrode casing and which is baked by electric current into an electrically conductive solid cylindrical form in the lower portion of the electrode casing. Electrical current is connected between three-phase electrode tips, and the arc formed between the electrodes will consume the baked electrode. The electrode is held by a slipping device that allows controlled displacement of the electrode.
The slipping device generally consists of two clamping rings which are sequentially operated and moved to extend the electrode as the tip of the electrode is consumed in use in the furnace. The two rings are connected with hydraulic cylinders that enable relative movement between the upper and lower clamping rings.
This action enables slipping through of the electrode casing whilst always maintaining a positive grip on the casing.
GB 262481 discloses an electrode holder in the form of a ring or frame provided with pistons by which clamping pressure is exerted on the electrode. Either the clamping or releasing movement of the pistons or both of such movements can be effected by fluid pressure. Alternatively, the clamping movement of the pistons can be affected by springs.
U.S. Pat. No. 4,154,974 A discloses a clamp assembly for suspending an arc furnace electrode, including a plurality of contact shoes adapted to bear against the surface of the electrode. The contact shoes are pivotally mounted adjacent their upper ends. Force producing means independent of the shoe support engages each contact shoe for forcing the same into high pressure engagement with the electrode.
U.S. Pat. No. 7,075,966 B2 discloses a slipping clamp assembly for holding an axially-extending electrode and for axially raising and lowering the electrode. The slipping clamp assembly comprises a first slipping sleeve for exerting a first clamping force on the electrode, a second slipping sleeve for exerting a second clamping force on the electrode, and a slipping clamp frame to which both slipping sleeves are connected. Both slipping sleeves are axially movable relative to the frame and independent on one another.
U.S. Pat. No. 7,095,777 B2 discloses an electrode slipping device arrangement including a lower electrode slip clamp surrounding the electrode and carried by a ring beam, an upper electrode slip clamp which is movable relatively to the lower clamp, slipping cylinders which are connected to and between both slipping clamps, and electrical load regulating cylinders which are connected to act between the ring beam and fixed structure above the furnace roof. The electrode column also includes at least one resiliently yieldable load resisting device which is located between the upper slip clamp and structure on the ring beam and on which the electrode, when clamped only by the upper slip clamp may totally be supported and means for measuring the load induced of the load resisting device. This slipping device arrangement allows monitoring of the length of the electrode.
In a slipping device comprising clamping shoes and clamping cylinders which are arranged to exert a normal force on the electrode, clamping cylinders need to be removed from time to time for maintenance or replacement purposes. Typically the clamping cylinder has to be dismantled in place, which is troublesome and time-consuming.